Recent advance in neuroscience is making clear the natural shape of neurotransmitters, substances deeply related to memory in the brain. It is said that some of these substances are neuropeptides containing prolines.
Recovery of the memory was reported by the dose of neuropeptide containing proline to an experimental amnesia rat (See Science 211, 601 (1981)). On the other hand, it is presumed that these neuropeptide - hormones shall be metabolized by cerebral endogenous peptidases. Especially, prolyl endopeptidase (EC, 3. 4. 21. 26) might take part in this metabolism closely (See J. Biochem., 94, 1179 (1983)).
From these facts, the studies were in progress that it should be possible to prevent or treat amnesia by inhibiting prolyl endopeptidase and suppressing the metabolism of neutrotransmitters. (See Protein, Nucleic acid and Enzyme 25(6), 513(1980); Nippon Nougei Kagaku Kaishi 58(11), 1147(1984); J. Neurochem., 41, 69(1983); ibid 42, 237(1984).)
For the purpose described above, several compounds were synthesized. For example, it is clear that N-benzyloxycarbonyl-glycyl-L-prolyl-chloromethane and N-benzyloxycarbonyl-L-prolyl-prolinal strongly inhibit prolyl endopeptidase (See J. Neurochem., 41, 69 (1983)). More recently, it is disclosed that compounds shown below are effective for the above purpose.
(i) Prolinal derivatives of general formula: ##STR5## [wherein A.sub.1 represents a protecting group of amino acid group in the field of amino acid chemical, and X.sub.1 represents a residual group of amino acid.]
(See Japanese Patent Kokai No. 60-188317, i.e. European Patent Publication No. 154353).
(ii) N-acylpyrrolidine derivatives of general formula: ##STR6## [wherein n2 represents a number of 1.about.4, and R.sup.a represents lower alkyl ester group, --CH.sub.2 OH group or aldehyde group.]
(See Japanese Patent Kokai No. 61-37764; a compound wherein n2 is 5 is also disclosed by correction, i.e. European Patent Publication No. 172458).
(iii) Compounds of general formula: ##STR7## [wherein A.sub.3 represents methyl group or benzyloxy group, R.sup.c represents isopropyl group or isobutyl group on condition that plural R's have the same meaning in one formula. And n3 represents 2 or 3.]
(See Japanese Patent Kokai No. 61-183297.)
Most recently, five applications related to anti-amnesia agents having prolinal skeltons were published. i.e.
(iv) Compounds of general formula: ##STR8## (wherein R.sup.d represents a group of --CH.sub.3, ##STR9##
(See Japanese Patent Kokai No. 61-238775, i.e. European Patent Publication No. 201741).
(v) N-acylpyrrolidine derivatives of general formula: ##STR10## [wherein R.sup.3e represents lower alkyloxycarbonyl group, hydroxymethyl group or formyl group, R.sup.1e represents a hydrogen atom or lower alkyl group, R.sup.2e represents phenyl group or a group of the following formula: ##STR11## (wherein R.sup.4e represents a hydrogen atom, a halogen atom or lower alkoxy group, R.sup.5e represents a hydrogen atom or lower alkyl group, n5 represents 0 or 1, A.sub.5 represents an oxygen atom, methylene group, hydroxymethylene group, phenylmethylene group or carbonyl group.) or R.sup.1e and R.sup.2e represent, together with, benzylidene group unsubstituted or substituted on its aromatic ring(s).]
(See Japanese Patent Kokai No. 61-238776, i.e. European Patent Publication No. 201742).
(vi) Compounds of general formula: ##STR12## [wherein n6 represents a number of 0.about.2. R.sup.1f represents a straight-chained organic group of from 5 to 25 carbon atoms which is saturated or unsaturated wherein an unsaturated carbon chain may contain plural number of double bonds. R.sup.2f represents a group of ##STR13## R.sup.3f represents lower alkyl ester group, --CH.sub.2 OH group or aldelyde group.]
(See Japanese Patent Kokai No. 61-238799, i.e. European Patent Publication No. 201743).
(vii) Compounds of general formula: ##STR14## (wherein n7 is an integer of more than one, R.sup.1g is a saturated or unsaturated straight-chained hydrocarbon group of from 5 to 25 carbon atoms. Herein said, unsaturates carbon chain may contain plural number of double bonds. R.sup.3g represents lower alkyl ester group of the formula: --COOR.sup.4g (wherein R.sup.4g represents lower alkyl group.), hydroxymethyl group or formyl group, R.sup.2g represents methyl group, phenyl group, hydroxyphenyl group, indolyl group, imidazolyl group, carboxyl group, formyl group, amino group, hydroxy group, hydroxyalkyl group, thiol group, methylthio group or guanidino group etc. and each of above groups may be substituted. R.sup.5g represents a hydrogen atom or a single bond between carbon atom and nitrogen atom together with R.sup.2g when n7 is 3.)
(See Japanese Patent Kokai No. 62-84058, i.e. European Patent Publication No. 201743).
(viii) Dipeptide derivatives of general formula: ##STR15## (wherein m represents an integer of 1.about.8, n8 represents an integer of 1.about.6, R.sup.1h represents a hydrogen atom, R.sup.2h represents a hydrogen atom, a branched alkyl group of from 3 to 5 carbon atoms, phenyl group, hydroxyphenyl group, indolyl group, imidazolyl group or methylthio group, or a single bond between carbon atom and nitrogen atom with R.sup.1h. R.sup.3h represents lower alkyl ester group, hydroxymethy group or formyl group.)
(See Japanese Patent Kokai No. 62-148467, i.e. European Patent Publication No. 201741).
And more, the present inventors have filed an application related to prolinal derivatives having an activity of anti-amnesia, in advance of the present application, i.e.
(ix) Prolinal derivatives of general formula: ##STR16## [wherein A.sub.9 represents alkylene or alkenylene group of from 1 to 8 carbon atom(s) or a saturated hydrocarbon ring of from 3 to 7 carbon atoms, R.sup.j represents hydrogen atom, phenyl group, benzyl group, alkyl group of from 1 to 8 carbon atom(s) or cycloalkyl group of from 3 to 7 carbon atoms, B.sub.9 represents alkylene group of from 1 to 8 atom(s) unsubstituted or substituted by phenyl group or benzyl group or a single bond, D.sub.9 represents carbocyclic or heterocyclic ring unsubstituted or substituted by from one to three of halogen atom, alkyl or alkoxy group of from 1 to 4 carbon atom(s), nitro group or trifluoromethyl group.] (See European Patent Application filed on 10th Nov., 1987.)